Metal-to-metal seals in electron discharge tubes



g 3, 1954 w. w. HANSEN HAL 2,685,125

METAL-TO-METAL SEALS IN ELECTRON DISCHARGE TUBES Original Filed Dec. 10, 1942 INVENTO 0.1..SNOW RS PV- W. HH/VSE/V BY A TTORNEY Patented Aug. 3, 1954 OFFICE METAL-TO-METAL SEALS IN ELECTRON DISCHARGE TUBES William W. Hansen,

Donald L. Snow, Sa

t Sperry Corporati ware Stanford University, and 11 Carlos, Calif-2, assignors on, a corporation of Dela- Original application December 10, 1942, Serial No.

68,603, now Patent No. 2,456,653, dated December 21, 1948.

Divided and this application October 16, 1948, Serial No. 54,872 4 Claims. (01. 29196.6)

seals in electronic and like devices. tronic apparatus it is frequently desired to make ponents of a cobalt-nickel-iron alloy of the type known variously by such trade names as Kovar and Fernico. This alloy is used because it has an extremely low coeflicient of thermal expansion and lends itself readily to adaptability in electronic apparatus.

According to one phase of the invention we erations of soldering members made of the above-considered cobalt-nickel-iron alloy to other metal parts. These joints must be mechanically strong and vacuum tight.

In securing such .alloy members together or to another metal we preferably employ a soldering operation, using a solder having an appreciable silver content and a relatively high melting point. We have found that this silver solder has an extremely high aifinity for the nickel-cobalt-iron alloy, and rapidly enters into combination with tween the cobalt-nickel-iron alloy and the silver in the solder, whereby the alloy member develops a relatively large newly alloyed and relatively necting a metal member in gas tight relation with another metal member and a glass body.

It is a further object of the invention to provide a high frequency device having efficient durale novel sealed joints which are resistant to the thermal and mechanical stresses encountered during normal operation of the device.

A further object of the invention is to provide a novel joint between two metal surfaces connected by a solder containing a metal which is readily alloyable with one or both of said surfaces, wherein formation of the alloy is avoided, and methods of making such a. joint.

A further object of the invention is to provide a novel joint between two metal surfaces connected by a solder containing a metal which is by first coating said one surface with a metal which prevents the solder from contacting said one surface.

A further object of the invention is to provide nickel-iron alloy wherein the alloy surface is coated before soldering with a layer of nickel or an equivalent protective coat.

Further objects of the invention will presently appear as the description proceeds in connection with the appended claims and the annexed drawings wherein:

Fig. 1 is a sectional view illustrating an electron tube embodying the invention.

Fig. 2 is an enlarged section of the Kovar-glass joint in the transmission line of Fig. 1.

Fig. 3 is an enlarged section illustrating the soldered metal to metal joint where the transmission line of Fig. 1 enters the resonator.

Fig. 4 is another enlarged section illustrating the soldered metal to metal joint between the tube barrel and the resonator.

This application is a division of our Patent No. 2,456,653, dated December 21, 1948.

Referring now more particularly to the figures, Fig. 1 illustarates the invention as applied to a tunable high frequency electronic tube of the trio transmission line.

The hollow resonator ll comprises a cylindrical metal barrel i2 and opposite end walls i3 and I 4 provided with reentrant poles I5 and I6 supporting centered and aligned grids l1 and 18. A suitable cathode I9 is located within pole 16 near grid l8.

Wall I4 is an annularly crimped sheet metal member of beryllium copper or a like resilient fatigue resistant material having sufificient stiiiness to normally maintain its shape but being controllably deformable for tuning. Wall i4 is secured permanently,- preferably by soldering, to barrel l2 and pole IS.

A metal plate 2| is rigid with pole IS below wall 14 and parallel to wall 13. Wall 13 and plate 2| which may be of steel, copper or any suitable metal, are interconnected by the usual springs (only one shown) urging them together and by adjustable tuning screws such as 22. As screws 22 are rotated, the distance between grids H and I8 is changed to tune the hollow resonator. Plate 2! is carried by the usual base (not shown).

The wall of barrel I2 is apertured at 23 to renator to provide an antenna loop 26, and is anchored, as by soldering, to the inner periphery of outer conductor 2%. Conductors 24 and 25 are preferably made of a cobalt-nickel-iron alloy such as Kovar, Fernico, or the like.

Conductor 25 is a relatively stiff wire held firmly centrally in the transmission line assembly by an annular seal ill of glass or some other rigid highly insulating materiaL'which also forms a gas tight seal for the conductor.

Wall i3 is formed with an annular groove 28 in which is seated and soldered one end of a cylindrical barrel 29, preferably of Kovar or its above mentioned equivalents. The other end of barrel 29 is enclosed by a glass envelope 30 sealed thereto along rim 3i so that the interior of the tube is gas tight for evacuation to operating condition.

The above discussed problems of making cilicient gas tight joints capable of withstanding the thermal and other mechanical strains at tendant to operation of such ultra high frequency apparatus have chiefly been solved by the inven tion, as embodied in the above, and'thesolutions will be ex in detail below.

Fig. 2 illustrates a greatly enlarged section through the glass-to-metal seal 21 in the concentric transmission lineoi Fig. 1. Such a glassto metal seal is particularly claimed in our patent No. 2,456,653.

Fig. 3 is an exaggerated sectional representation of the .metal-to-metal joint between the Kovar tube barrel :29 and wall 1 3. The lower edge and periphery of collar 29 are coated, as by distillation or electrodeposition, with a layer of nickel 39. The nickel-plated end of collar 29 is inserted and silver soldered in the usua12mannor in groove .28, the hardened solder body being indicated at in Fig. 3.

This above soldered oint is sound and firm, and the barrel does not fracture under repeated temperature stress. The nickel coating does not rapidly alloy with the silver in the solder, and prevents the silver from reaching the Kovar. It is obvious that any suitable metal other than nickel may beused to plate in Kovar. It is essential, however, that such metal be capable of forming a good solder bond and also serve as a protectiveshield for preventing the .silver solder from alloying with the Kovar. The metal'plat ing should, of course, have a higher melting point than the solder. One such :metal which might be used place of nickel is palladium.

Fig. i is an exaggerated sectional illustration of the manner in which Kovar conductor 24 is mounted on barrel l2.

Prior to insertion into aperture 23, the associated end of conductor 2 1 is coated on its external periphery, preferably by electrodepcsi with a layer 3! of nickel. The

of conductor 21% is thrust into aperture and silver soldered in the usual manner, the hardened body of Solder being indicated at 98-.

The phase of the invention related to Figs. .3 and l is of especial application and advantage where the soldered parts are relatively large or subjected to relatively heavy stresses.

Since many changes could be made'in'the above construction and many apparently widely 'dif ferent embodiments of this invention'could be made without departing from the scope thereof,- it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense,

What is claimed is:

l. The method of joining together two metal members for assembly into a vacuum-tight structure of an electron discharge tube or the like, at least one of said metal members consisting of an alloy of the class commercially known as Kovar and comprising as its principal constituents cobalt, nickel, and iron, in the proportion of 10 to 20 percent cobalt, 20 to 35 percent nickel,

and the balance substantially iron, with other elements being of the order of 1 per cent or less, the method including the steps of plating the Kovar member with a thin layer of nickel over the area to be joined to the other member to provide barrier against intergranular penetration-o'i silver into the Kovar member, and silver soldering the other member thereto with a hard solder comprising copper an appreciable amount of silver.

2. The .niethod of joining two metallic members together where one of said members consists of analloy of 10 to 20 percent cobalt, '26 to 35 per cent nickel, and the balance substantially iron, said alloy memberbeing part or a dividing will between regions or" high and low pressure of an electron discharge tubeor tae like, the'method including the steps of plating a thin nickel layer on said alloy member, and melting a solder containing high percentage of silver between the coat dsurface of the alloy membe and the other ielnber for joining the two members structurally, the nickel layer serving to prevent physical cracking of the alloy by intrusion of the silver into the member with resultant leakage between the high and low pressure regions.

l'na vacuurmtight envelope for an electron discharge tube or the like, the combination or a first metallic member and a second metallic membenthe first metallic member being an alloy including 28 to 35 percent nickel, if) to 20 percent cebalt'and the balance substantially of iron, a thin layer of nickel on the surface of the alley member, and a bedy of hardsclder haying a high percentage of silver joining the two members in a gas-tight joint, the layer or" nickel separating the body or" hard solder from the alloy member to prevent penetration of the silver into the alloy.

i. A gas-tight joint an eectron 'discha'rge tube'or like-compl sing a first metallic member of an alloy including 20 to 35 percent-nickel, 10 to as percent cobalt, and the balance substantially of inn, a second metallic member, a thin layer or "r on the member in the region of the joint, andabcdy-of solderincluding a high pence-stage of silver between thesecond member and the layer of nickel, said layer of nickel separating the "body of solder from the first member to prevent penetration of the silver into the alloy.

References Cited in 'the'nle or this patent UNITED STATES PATENTS 

1. THE METHOD OF JOINING TOGETHER TWO METAL MEMBERS FOR ASSEMBLY INTO A VACUUM-TIGHT STRUCTURE OF AN ELECTRON DISCHARGE TUBE OR THE LIKE, AT LEAST ONE OF SAID METAL MEMBERS CONSISTING OF AN ALLOY OF THE CLASS COMMERCIALLY KNOWN AS KOVAR AND COMPRISING AS ITS PRINCIPAL CONSTITUENTS COBALT, NICKEL, AND IRON, IN THE PROPORTION OF 10 TO 20 PERCENT COBALT, 20 TO 35 PERCENT NICKEL, AND THE BALANCE SUBSTANTIALLY IRON, WITH OTHER ELEMENTS BEING OF THE ORDER OF 1 PER CENT OR LESS, THE METHOD INCLUDING THE STEPS OF PLATING THE KOVAR MEMBER WITH A THIN LAYER OF NICKEL OVER THE AREA TO BE JOINED TO THE OTHER MEMBER TO PROVIDE A BARRIER AGAINST INTEGRANULAR PENETRATION OF SILVER INTO THE KOVAN MEMBER, AND A HARD SOLDERING THE OTHER MEMBER THERETO WITH A HARD SOLDER COMPRISING COPPER AND AN APPRECIABLE AMOUNT OF SILVER.
 3. IN A VACUUM-TIGHT ENVELOPE FOR AN ELECTRON DISCHARGE TUBE OR THE LIKE, THE COMBINATION OF A FIRST METALLIC MEMBER AND A SECOND METALLIC MEMBER, THE FIRST METALLIC MEMBER BEING AN ALLOY INCLUDING 20 TO 35 PERCENT NICKEL, 10 TO 20 PERCENT COBALT, AND THE BALANCE SUBSTANTIALLY OF IRON, A THIN LAYER OF NICKEL ON THE SURFACE OF THE ALLOY MEMBER, AND A BODY OF HARD SOLDER HAVING A HIGH PERCENTAGE OF SILVER JOINING THE TWO MEMBERS IN A GAS-TIGHT JOINT, THE LAYER OF NICKEL SEPARATING THE BODY OF HARD SOLDER FROM THE ALLOY MEMBER TO PREVENT PENETRATION OF THE SILVER INTO THE ALLOY. 